We present a compact cold-atom clock configuration where isotropic laser cooling, microwave interrogation, and clock signal detection are successively performed inside a spherical microwave cavity. For ground operation, a typical Ramsey fringe width of 20 Hz has been demonstrated, limited by the atom cloud’s free fall in the cavity. The isotropic cooling light’s disordered properties provide a large and stable number of cold atoms, leading to a high signal-to-noise ratio limited by atomic shot noise. A relative frequency stability of $2.2\times {10}^{-13}{\tau }^{-1/2}$ has been achieved, averaged down to $4\times {10}^{-15}$ after $5\times {10}^3$ s of integration. Development of such a high-performance compact clock is of major relevance for on-board applications, such as satellite-positioning systems. As a cesium clock, it opens the door to a new generation of compact primary standards and timekeeping devices.

• Received 8 July 2010

DOI:https://doi.org/10.1103/PhysRevA.82.033436